In the preparation of ampicillin, with 6-APA being acylated with a D-phenylglycine derivative, the recovery of the ampicillin and working up of the reaction mixture are difficult in general.
A process for isolating the ampicillin pure from a mixture containing ampicillin and minor quantities of 6-APA is described in JP-A-47030687. According to the process described in this Japanese publication, an acid aqueous mixture containing 6-APA and ampicillin is subjected to an extraction with butanol or isoamylalcohol, after which the pH is raised to a value between 6 and 7 and the product is recovered by complete boiling down and freeze-drying. The drawback of this method is that organic solvents that are alien to the process have to be added. In addition, complete boiling down and freeze-drying is not industrially practicable. Moreover, the process involves formation of salts that are included in the freeze-dried product.
GB-A-994402 discloses a process wherein ampicillin is recovered from a mixture of ampicillin and amino-penicillanic acid by conversion of the ampicillin to the trialkylamine salt and recover the ampicillin as its trialkylamine salt.